The Inflamed Mind summary

Since the beginning of time, humans have been at war. With one another often enough, but also against the thousands of tiny non-human invaders that swarm our bodies on a daily basis. The immune system doesn't only activate when we get a cold. Day and night, our immune systems defend us against hostile bacteria, germs, bugs, pathogens, viruses and worms – collectively called antigens – which could otherwise lead to serious illness or death.

The human immune system consists of various parts and structures. Its most important soldiers are white blood cells, which can be divided into different types of specialized immune cells such as macrophages, and lymphocytes.

In his early training as a physician, the author treated an older lady for her rheumatoid arthritis. Because the woman seemed very depressed, he questioned her about her mood and social life during the examination. Back then, he didn’t suspect that the inflammation underlying her arthritis could also be causing her depression – but he felt it was important to address all of her issues holistically. 

After the examination, the author was sternly told by his supervisor that it was his job to treat the lady’s arthritis, not her depression. After all, anyone with such an awful disease would probably be a little depressed.

If you’re an ironclad Cartesian dualist, the notion that you can cure the mind by tweaking chemicals in the brain is inconceivable. 

But today, antidepressant drugs that claim to balance the chemical composition of the brain have become one of the few treatment options for depression. 

Around the time Prozac launched in the '90s, the first papers linking depression to the immune system were published in obscure medical journals. They included titles such as "The Macrophage Theory of Depression" (1991) and "Evidence for an Immune Response in Major Depression" (1995). In hindsight, these theories seem like a massive breakthrough. But at the time, they were largely ignored – they didn’t fit the new serotonin story.

Nevertheless, these papers marked the beginning of two new medical fields of research: neuroimmunology, which studies the link between the immune system and the brain; and immunopsychiatry, which focuses on the connection between the immune system and mental health. 

Just a few decades ago, scientists were convinced that it was nearly impossible for the immune system to affect our brain. They thought the brain had its own, completely separate immune system, shielded from the rest of the body by the so-called Blood-Brain Barrier, or BBB. The BBB is a dense wall of cells that surrounds the brain and prevents molecules circulating in the blood from directly passing through to the brain. 

But in recent years, scientists have discovered that the BBB isn’t as impermeable as previously thought. Not only are there gaps between the BBB cells that allow certain molecules and proteins to enter the brain; the cells themselves can respond to inflammatory signals of the body, and pass that information on to the brain.

So far, we’ve learned that inflammation is a natural response of the immune system, but it causes serious collateral damage to our bodies and brains when it becomes chronic. This, in turn, affects our moods, thoughts and behavior.

But what causes chronic inflammation?

Now that you’ve learned about how inflammation can cause depression, you probably want to know why this is the case. 

When we ask why our bodies and brains do this or that, the answer will usually be natural selection. If we adhere to Darwin’s evolutionary theory, then somehow, at some point in human evolution, inflammation and depression must have helped the human species survive.

If you suspect that your depression is caused by inflammation after reading these blinks, you probably want to know what you can do about it. 

Unfortunately, professional treatment options for inflammatory depression are still limited.